Step $2$

$We$ must find $d\frac{z}{d}t.$ Differentiating both sides and simplifying gives $us$ the following.

$\frac{dz}{dt}=2x*\frac{dx}{dt}+2y$

$\frac{dz}{dt}=8,\frac{dy}{dt}$

$(x*\frac{dx}{dt}+*\frac{dy}{dt})$